Start from scratch with the schematic. There are 2 diodes, maybe one was put in backwards. The grounds go to different places so they cannot be tied together. IIRC one cathode end of one diode goes to the ballast, pin5 , and the other to pin 4 of the ballast provided you are using the correct ballast . The cathode end of the diode going to pin 5 now continues to the positive end of the second diode. Check that schematic it's all there as it could be a simple mistake or a wire in the wrong place. I have 7 of these sets and had my share of stupid mistakes.